ScienceDaily

Saturday, September 21, 2002

Philadelphia, PA -- There is a sound neurological basis for the cliché that men are more aggressive than women, according to new findings by scientists at the University of Pennsylvania School of Medicine. Using magnetic resonance imaging (MRI) scans, the Penn scientists illustrated for the first time that the relative size of the sections of the brain known to constrain aggression and monitor behavior is larger in women than in men.

The research, by Ruben C. Gur, PhD, and Raquel E. Gur, MD, PhD, and their colleagues in Penn's Department of Psychiatry and the Department of Epidemiology, is published in the recent issue of the Journal of the Cerebral Cortex.

The findings provide a new research path for therapies that may eventually help psychiatric patients control inappropriate aggression and dangerous patterns of impulsive behavior. They also bolster previous work by the Gurs demonstrating that although some gender differences develop as result of adaptive patterns of socialization, other distinctions are biologically based and probably innate.

"As scientists become more capable of mapping the functions of activity in various parts of the brain, we are discovering a variety of differences in the way men and women's brains are structured and how they operate," said Ruben Gur, first author of the study.

"Perhaps the most salient emotional difference between men and women, dwarfing all other differences, is aggression," he said. "This study affords us neurobiological evidence that women may have a better brain capacity than men for actually 'censoring' their aggressive and anger responses."

In the Gurs' work, they relied on established scientific findings that human emotions are stimulated and regulated through a network that extends through much of the limbic system at the base of the brain (the region encompassing the amygdala, hypothalamus and mesocorticolimbic dopamine systems), and then upward and forward into the region around the eyes and forehead (the orbital and dorsolateral frontal area), and under the temples (the parietal and temporal cortex).

The amygdala is involved in emotional behavior related to arousal and excitement, while the orbital frontal region is involved in the modulation of aggression.

The Gurs' study measured the ratio of orbital to amygdala volume in a sample of 116 right-handed, healthy adults younger than 50 years of age; 57 subjects were male and 59 were female. Once the scientists adjusted their measurements to allow for the difference between men and women in physical size, they found that the women's brains had a significantly higher volume of orbital frontal cortex in proportion to amygdala volume than did the brains of the men.

"Because men and women differ in the way they process the emotions associated with perception, experience, expression, and most particularly in aggression, our belief is that the proportional difference in size in the region of the brain that governs behavior, compared to the region related to impulsiveness, may be a major factor in determining what is often considered 'gendered-related' behavior," Raquel Gur said.

Others Penn investigators participating in the study were Faith Gunning-Dixon, PhD, and Warren B. Bilker, PhD, of the Department of Epidemiology.

The study was funded by a grant from the National Institutes of Health.